This invention relates to magnetic performance measurement of a merged type magneto-resistive head during the read process in a disk drive, including at least any of the collection comprising AMR (Anisotropic Magneto-resistive), GMR (Giant Magneto-resistive), and TMR (Tunneling Magneto-resistive) read-write head.
Disk drives are an important data storage technology, based on several crucial components. These components include the read-write heads, which directly communicate with a disk surface containing the data storage medium. This invention involves magnetic performance measurement of the read-write heads inductively using the write heads.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator arm 30 with voice coil 32, actuator axis 40, suspension or head arms 50-58 with slider/head unit 60 placed among the disks.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with actuator 20 including actuator arm 30 with voice coil 32, actuator axis 40, head arms 50-56 and slider/head units 60-66 with the disks removed.
Since the 1980""s, high capacity disk drives 10 have used voice coil actuators 20-66 to position their read-write heads over specific tracks. The heads are mounted on head sliders 60-66, which float a small distance off the disk drive surface when in operation. Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move head arms 50-56 positioning head slider units 60-66 over specific tracks with speed and accuracy. Actuator arms 30 are often considered to include voice coil 32, actuator axis 40, head arms 50-56 and head sliders 60-66. Note that actuator arms 30 may have as few as a single head arm 50. Note also that a single head arm 52 may connect with two head sliders 62 and 64.
Merged type heads possess different components for reading and writing, because the magneto-resistive effect only occurs during reading. A merged type head typically includes a thin film head and a spin valve sensor. The primary use of the thin film head is in the write process. The spin valve sensor is used for reading.
MR heads have several advantages over earlier approaches, using a single component, for both read and write. Earlier read-write heads were a study in tradeoffs. The single component, often a ferrite core, can increase read sensitivity with additional windings around the core. However, these added windings make the ferrite core write less efficiently.
Introduced in the 1990""s, merged heads brought significant increases in areal density. A merged type head reads the disk surface using a spin valve, containing a conductive thin film, whose resistance changes in the presence of a magnetic field. By separating the functions of writing and reading, each function can be optimized further than would be possible for the older read-write heads. For all the improvement that merged heads bring, their control to date creates problems. However, before discussing these problems, consider first how and what controls these devices in contemporary disk drives.
FIG. 2A illustrates a simplified schematic of a disk drive controller 1000 controlling an analog read-write interface 220, the read differential signal pair (r+ and rxe2x88x92) and write differential signal pair (w+ and wxe2x88x92) communicating the resistivity found in the spin valve within MR read-write head 200 of the prior art.
FIG. 2B illustrates a suspended head slider 60 containing the MR read-write head 200 of the prior art.
FIG. 2C illustrates a perspective view of merged read-write head 200 from FIG. 2B including write inductive head 202 and magnetoresistive read head (or spin valve) 204 of the prior art.
FIG. 2D illustrates a simplified cross section view of spin valve 204 of FIG. 2C of the prior art.
FIGS. 3A and 3B illustrate the magnetic flux direction related to the charging of the write differential signal pair connecting to P1 and P2 of the prior art.
FIG. 3A illustrates the field flowing from P1 to P2, when there is a positive write current asserted on the write differential signal pair under normal conditions in the prior art.
FIG. 3B illustrates the field flowing from P2 to P1, when there is a negative write current asserted on the write differential signal pair under normal conditions in the prior art.
Electro-Static Discharge (ESD) can diminish or damage these flows by pinning part of the spin valve head 204 in a weakened or reversed magnetic condition. Such conditions damage or destroy the ability of the spin valve 204, thus the MR read-write head 200 to function.
FIG. 4A depicts the voltage amplitude measured across the read differential signal pair sensing a written pulse on a disk drive surface in the prior art.
As used in the prior art, the amplitude is defined as v++vxe2x88x92. Asymmetry is defined as v+xe2x88x92vxe2x88x92. The quality measure for spin valves is asymmetry vs. amplitude, or
(v+xe2x88x92vxe2x88x92)/(v++vxe2x88x92).
The ideal situation would have a quality measure of 0%, but acceptable ranges are often 5% to 10%, with 7% being typical for a spin valve. Note that ESD damage is indicated by increases in the quality measure.
Typically, either a quasi-static tester or R(H) tester is used to test the spin valve for ESD damage. Both forms of testers require external magnets, often generating at least 1,000 Oesteds. The external magnets further require power supplies, and a mechanical infrastructure to accurately position the magnet with respect to these very small components. All of this adds to the cost of testing and therefore manufacturing MR read-write heads, as well as the products containing these read-write heads, including head sliders, actuator arms, voice coil actuators and disk drives.
Another alternative is the use of a disk media based tester such as manufactured by Guzik. While somewhere in the process of making a voice coil actuator, testing must be done using disk media, this is even more expensive than quasi-static or R(H) testing.
To summarize, what is needed are test circuits and methods reducing the cost of testing and manufacturing MR read-write heads, and products containing these read-write heads (head sliders, actuator arms, voice coil actuators and disk drives).
The invention includes a test system and method determining performance of a merged magnetoresistive read-write head based upon operating the write inductive head and measuring the resistance of the read head under certain read current bias conditions selecting read heads undamaged by ESD.
The invention removes the requirement for an external magnet or disk memory media surface to determine whether a merged magneto-resistive read-write head has been damaged by Electro-Static Discharge (ESD).
The system and method can be applied at the wafer fabrication manufacturing stage to the read-write heads, as well as the assembly stages for head sliders, actuator arms, and voice coil actuators. The invention includes the products of these manufacturing stages using the method, as well as disk drives assembled from these components.
This invention significantly reduces production cost of testing for ESD damage.
Note that the inventive method can be implemented at least in part by the operation and control provided by one or more of the following: a computer, a finite state machine, a neural network and/or a human operator. While the following discussion is focused on computer operations, this has been done strictly to clarify the discussion and is not meant to limit the scope of the claims.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.